1. Field of the Invention
This invention relates generally to plug members adapted to provide a seal closure in an apertured workpiece and more particularly to a precoated plug for sealing an opening for the core holes in water jackets of internal combustion engines and other similar manufacturing holes, and to a method for applying a plastic coat to the peripheral surface of such plug members.
2. Description of the Prior Art
The cylinder block of an internal combustion engine is usually provided with a water jacket which in many cases is cast integral with the cylinder. This jacket generally has a plurality of holes passing therethrough to the outside which have been provided for removing the sand cores after the block has been cast. They are ordinarily provided with a sealing plug secured therein by friction so as to provide an enclosed cavity.
It may also be necessary to drill access holes or passages in a casting in order to permit internal machining or to provide for cross connecting internal fluid carrying passages and the like. It is usually necessary to close off these access holes or passages in order to preclude introduction of foreign matter internally of the part and to prevent fluid leakage therefrom. One of the current methods of closing off such access holes in passages has been the forcing of a short metal rod into the end of the passage. Although this method is satisfactory in certain applications, it is quite unsatisfactory under circumstances where fluid under pressure is subsequently introduced into the passage inasmuch as the rod may be forced out of the hole or the passage by the pressurized fluid.
A variety of methods have been employed to provide a satisfactory sealing plug which is reliable and inexpensive. Such prior methods have included the use of a plug having a diameter larger than the opening it is to close, at least to the extent that there will be a relatively large compressive engagement between the plug and the opening. In order to insert the rod into the opening without cracking the workpiece it is sometimes necessary to heat the area of the workpiece about the opening or to cool the rod to cryogenic temperature prior to insertion. This type of sealing means results in a relatively expensive operation and is difficult to use on high volume production. Other methods have consisted in tapping the access hole and threading a bolt or threaded plug therein. Such methods are relatively time consuming and therefore expensive from a production standpoint, and it is also possible that fluid pressure behind the plug may result in leakage past the threads to the outside of the casting.
Specifically in the automotive industry, core openings are generally sealed by means of plugs which are press fitted within the openings. Prior to the press fitting of the plugs within the openings, the openings are coated with an adhesive material by an operator. Although such a method is satisfactory, it does require two steps, that is, the manual coating of the opening and the insertion of the plug generally by means of an automatic plug inserting machine. Since the coating is applied manually this sometimes leads to an improper coating of the part by the operator, and thus a proper seal between the plug and the opening is not achieved. Furthermore, existing adhesive coatings utilized in the automotive industry tend to become brittle and chip off in a relatively short period, thus losing the desired seal. Such existing adhesive coatings are subjected to oil, oil additives, water, anti-freeze and high temperature, all of which lead to a short sealing life.
It would therefore be very desirable to provide a plug for sealing an access hole in a metallic casting and the like in which the plug has been precoated with a plastic-like material so as to provide and insure a fluid tight seal upon insertion of the plug within the opening.